The external ear differs greatly in size and form in the various breeds;
in most it is relatively wide and thin and the greater part of it hangs
down over the opening. The anterior border has a prominence (Spina
helicis) at its lower part, and below this it divides into two branches
(Crura helicis). One of these continues down to a blunt point, while the
other turns in to the cavity of the concha. The posterior border forms a
pouch below its middle, and is thick and rounded in its basal part. Here
the conchal cartilage bears a pointed process (Processus uncinatus),
which projects upward and backward. The outer wall of the cavum conchæ
is supported by a quadrilateral plate (Tragus) above and a semiannular
cartilage below. The concave surface presents several cutaneous folds,
and in the cavum conchæ there are ridges and irregular prominences.
There are long hairs on the borders, apex, and the folds of the concave
surface, but the skin of the cavum conchæ is bare. The annular cartilage
is a complete ring. The osseous external auditory meatus is wide and
extremely short.
The auricular muscles are thin. The scutularis is extensive and is
divisible into interscutularis and fronto-scutularis. It partly covers
the occipitalis muscle, which is oval and unpaired and ends in the
fascia of the frontal region. The scutulo-auriculares superficiales,
inferior et accessorius, and the cervico-scutularis are not
differentiated as separate muscles. The cervico-auricularis
superficialis and the parieto-auricularis both bifurcate and are
inserted into the base of the concha and the scutiform cartilage. The
parotido-auricularis is narrow and almost long enough to meet the
opposite muscle. The tragicus consists of two parts; of these the
lateral one is long and arises from the border of the mandible above the
angular process. The helicis and the verticalis auriculæ are well
developed.
The tympanic cavity is very roomy, extending ventrally into the large
but simple cavity of the bulla ossea. The tympanic membrane is extensive
and oval. The promontory is very pronounced. The auditory ossicles are
large. The Eustachian tube is short, and has a fibrous outer wall. Its
pharyngeal opening is an oblique slit situated on the lateral wall of
the naso-pharyngeal meatus, and is margined internally by a thick mucous
fold.
The cochlea has three and a half turns and is more sharply pointed than
in the ungulates.